1. Field of the Invention
The present invention relates to the design of battery assemblies, and more particularly to a corner tab termination design for lithium-polymer battery applications.
2. Description of the Prior Art
Presently there is a high level of interest in industry in designing thin layer solid state batteries. Such batteries are used in lap-top computers and other portable electronic devices. One particular type of thin layer solid state battery which is widely used is the lithium anode cell. The lithium anode cell comprises a lithium anode layer, a transitional metal oxide polymer composite cathode layer, and a solid or liquid electrolyte which includes a dissolved salt. Where the anode employed is made of lithium, the electrolyte would include a lithium salt. Batteries with anodes made of metals other than lithium, such as magnesium, have also been proposed.
An example of a conventional lithium flat cell battery is described in U.S. Pat. No. 4,997,732 to Austin, et al. ("Austin"), which is incorporated herein by reference in its entirety. FIGS. 3B and 5 of Austin have been incorporated as FIGS. 1 and 2 respectively in the present application, and are illustrative of the conventional lithium cell design. FIG. 2 shows a conventional bi-cell lithium battery 10. The battery body is comprised of various layers 26 shown in FIG. 1. In the center of the battery body 26 is anode assembly layer 112, which comprises a layer of lithium bonded to a layer of current collecting material. The anode current collecting material is typically copper foil. As illustrated in FIG. 1, the anode assembly layer 112 is interposed in between electrolyte layers 116. Electrolyte layers 116 are, in turn, interposed between cathode layers 120. Finally, cathode layers 120 are interposed between cathode current collector layers 124. The cathode current collector material is typically made of aluminum.
Also shown in FIG. 1 are cathode and anode terminals 134 and 132. The cathode terminal 134 is attached to cathode current collector 124. Similarly, anode terminal 132 is attached to the metal foil of anode layer 112. The layers of the battery body and the cathode and anode terminals are then packaged to form a flat bi-cell battery 10 as shown in FIG. 2.
One objective of the thin layer solid state battery shown in FIG. 2 is to be as thin and as compact as possible while at the same time maximizing the storage capacity, energy density, and shelf life of the battery. However, as shown in FIG. 2, the energy density and storage capacity of a conventional flat cell battery are not maximized since much of the battery volume is not used for housing the plurality of battery layers 26, but rather is used for housing the cathode and anode terminals 132 and 134. In addition, the proximity and location of the anode terminal relative to the cathode terminal may lead to inadvertent external short-circuit of conventional flat cell batteries.
It is therefore an objective of the present invention to maximize the storage capacity and energy density of flat cell batteries. An additional objective of the present invention is to locate the cathode and anode terminals relative to one another such that the potential for external short-circuiting is minimized.